Transmitting and receiving media packet streams

ABSTRACT

This invention concerns the transmitting and receiving of digital media packets, such as audio and video channels and lighting instructions. The network ( 104 ) is comprised of at least a transmitter device ( 110 ) and a receiving device ( 112 ). The controllers ( 122 ) and ( 126 ) of these devices handle the exchanging of configuration messages between the devices ( 110 ) and ( 112 ). Using the invention, the user is not required to manually configure the processor to receive media packet streams. Instead, a controller ( 126 ) of a receiving device ( 112 ) operates to receive information on a user selection of media channels and automatically configure the processor of the transmitter device. Further, the receiving device ( 112 ) is able to receive media channels using both unicast and multicast protocols. Media channels can be given textual labels which are unique on the unique ( 104 ) and easily identify to the user the actual source of the media channel. Media channels of different formats to be sent on the same net work simultaneous. Further, redundant media channels are easily accommodated.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/308,187, which was filed on Oct. 28, 2009, which is the NationalPhase application of International Application No. PCT/AU2007/000668,filed May 17, 2007, which designates the United States and was publishedin English. These applications, in their entirety, are incorporatedherein by reference.

TECHNICAL FIELD

This invention concerns the transmitting and receiving of digital mediapackets, such as audio and video channels and lighting instructions. Forexample, but not limited to, the invention concerns the use of anInternet Protocol (IP) computer network to transmit media channelsgenerated by media devices in a manner that meets high fidelityrequirements. The media channels are transmitted as media packets from atransmitter device to a receiver device for playout. The inventionconcerns a transmitter device, a receiver device, instruction messages,methods of receiving and transmitting media packet streams, computersoftware to perform these methods and a data network.

BACKGROUND ART

Media channels, such as audio and video channels, have long beentransmitted using application specific cables. For instance, two-corespeaker cable is used to carry left and right audio channels fromamplifiers to speakers.

More recently, media signals have been transmitted on computer basednetworks using protocols such as unicast or multicast. Unicast is amethod of sending packets on a computer network to a single destination.The unicast packets must be retransmitted for every media device thatwishes to receive the packets.

Multicast is typically used to refer to IP multicast, which is aprotocol for efficiently sending to multiple receiver devices at thesame time on TCP/IP networks by use of a multicast address. The computernetwork then operates to route the packets to each of the devices on thenetwork that wish to receive the multicast packets.

Examples of computer based network designed to transport digital mediais the computer network marketed by Telos. The Telos computer networkoperates using the multicast protocol and carries one channel ofinformation per multicast stream of packets. All data transmitted on thecomputer network is homogenous. Each packet contains samples from asingle channel, and all channels transmitted over the network use a 48kHZ sampling rate and 20 bits of data per sample. By keeping the packetand sample formats homogeneous the Telos system always knows how tointerpret an incoming packet. All it needs to know is which multicastaddress corresponds to each channel.

Another computer network marketed by CobraNet uses a unicast protocol.Transmitters are given repeating time intervals to transmit packets andthe receiver is configured to receive the packets during that particulartime interval.

SUMMARY OF THE INVENTION

In first aspect, the invention provides a receiver device for receivingmedia packet streams from a data network, the receiver devicecomprising:

-   -   a data interface to receive media packet streams, each media        packet stream containing one or more user selected media        channels;    -   a processor to extract the user selected media channels from the        received media packet streams; and    -   a controller to receive information on a user selection of media        channels advertised on the data network, to receive information        on the transmission source of each of the user selected media        channels so as to group the user selected media channels that        can be transmitted from the same transmission source, and to        automatically provide instructions to the processor that one or        more media packet streams are to be received for each group and        the number of user selected media channels in each media packet        stream.

In this way, the user is not required to manually configure theprocessor to receive media packet streams. Instead, the controlleroperates to receive information on a user selection of media channelsand automatically configures the processor. Further, the receiver deviceis able to receive media channels using both unicast and multicastprotocols using the invention. The invention has the advantage of beingable to use low cost data network cabling and equipment, such asswitched Ethernet, on which to receive the media packet streams.

The selected media channels each have a format and the controller mayoperate to receive information on the format of each of the selectedmedia channels. The format of a media channel may include any one ormore of sample rate, bit depth and encoding method. The controller mayalso group the selected media channels having the same format. Thisgrouping on format may be on any one or more of sample rate, bit depthand encoding method. Alternatively, media channels having differentmedia channel formats may be included within the one media packetstream. In this way the data network of the invention offers improvedflexibility since the receiver device is able to receive heterogeneousmedia channels from the same data network.

Each packet of a media packet stream may contain more media channelsthan the selected media channels of a group.

The one or more media packet streams of a group may also contain mediachannels that are not selected media channels of that group. Thecontroller may provide instructions to the processor that two or morepacket streams are to be received for each group.

The controller may be remote from the processor and or data interface.

Information about the transmission source may include network parametersof the transmission source. The transmission source may be atransmitting device. The network parameters may include an IP addressand configuration port identifier.

The controller may also receive for each selected media channelinformation on the methods in which the selected channel can bereceived. A method the selected media channel can be received may bewithin one or more pre-defined media packet streams that also containother media channels. The pre-defined media packet stream may bereceived using the multicast protocol.

Receiving the selected media channel may use unicast protocol and onrequest to the transmission source. The controller may further operateto send to the transmission source a request to receive a media packetstream containing the one or more selected media channels of a group.

The controller may determine the preferred method of receiving theselected media channel. This may include determining whether the mediachannels in a pre-defined media packet stream includes other selectedmedia channels, and favouring receiving the pre-defined media packetstream as the number of selected media channels within the pre-definedmedia packet stream increases. The controller may also receive aweighting factor for methods that the selected media channel can bereceived and favouring the method that has the weighting factor thatindicates the preferred method.

The controller's instructions to the processor may include instructionsto ignore one or more media channels within a media packet stream to bereceived.

The controller's instructions to the processor may include instructionson which output channels the extracted selected media channels should berouted to.

The controller's instructions to the processor may include instructionsas to the destination address and port to use, or equivalent addressinginformation for non-Internet Protocol transports.

The receiver device may include two or more data interfaces and thecontroller's instructions to the processor may include information onwhich data interface a media packet stream will be received. Thecontroller may further operate to send a request to the transmissionsource to receive a first media packet stream at a first data interfaceand a second media packet stream at the second data interface, whereinsamples contained in the first and second media packet stream are thesame.

The media channels may be advertised on the network as a unique namethat describes in words the source of the media channel. The informationthe controller receives on the user selection of media channels may bean indication of the unique name of each user selected channel. The namemay be comprised of one or more words that describe the source of themedia channel and the one or more words that describe the transmissionsource that will transmit the media channel. This enables the user toeasily browse and unambiguously identify the desired media channels.

The controller may send the advertised name of the media channel as alook-up-key to a database connected to the data network and to receivein reply the media channel format information from a database connectedto the data network. The database may be a distributed database.

The receiver device may include a second data interface, and thecontroller may provide instructions to the processor that a copy of amedia packet stream is to be received at the second data interface.Multiple second data interfaces may be provided. The user interface maybe located remotely on the data network from the processor. This enablesthe user to configure all the receiver devices from the one location onthe data network.

The controller may include storage means to store details of the groupsand method by which the media channels of the groups are to be received.This includes information about the transmission source of the group andformat of the media channels within the group.

The media channels may be audio signals, video signals, or instructionsignals, such as lighting instruction signals.

The data network may be implemented over the Internet Protocol. The datanetwork may be implemented with another packet-based transmissionmethod. The network may be comprised of sub-networks each havingdifferent packet-based transmission methods.

A media packet stream may contain distinct or overlapping media channelshaving different bit depths, encodings and sample rates. A single mediapacket stream may use some or all of the space in a packet.

In a second aspect the invention provides receiving media packet streamsfrom a data network, the method comprising the steps of:

receiving information on a user selection of media channels advertisedon the data network;

receiving information on the transmission source of each of the userselected media channels so as to group the user selected media channelsthat can be transmitted from the same transmission source;

automatically providing instructions to the processor that one or moremedia packet streams are to be received for each group and the number ofuser selected media channels in each media packet stream;

receiving the one or more media packet streams; and

extracting the user selected media channels from the received mediapacket streams.

In a third aspect the invention is an instruction message sent from thecontroller to a processor of a receiver device. In a fourth aspect theinvention provides computer software to perform this method.

In another aspect, the invention provides a transmitter device fortransmitting media packet streams on a data network, the transmitterdevice comprising:

-   -   a plurality of input media channels to receive media channels,        each media channel having a format;    -   one or more transmission ports to transmit media packet streams;    -   a processor to packetize received media channels to create media        packet streams for transmission by the transmission port; and    -   a controller to group received media channels having the same        format or to receive instructions on which received media        channels comprise a group; and to automatically provide        instructions to the processor to packetize media channels of a        group into the same media packet stream.

The controller may further operate to receive further instructionsamending which received media channels comprise a group. In this way thegroups can be dynamically amended over time.

The controller may further operate to provide further instructions tothe processor that a media packet stream is to be sent from twotransmission ports, such as two data interfaces—primary and redundant.

The controller may control the processor by sending to the processor aninstruction message. The controller may further control the processor toaddress the media packet stream to an address and port. The address maybe a multicast address or a unicast address (i.e. a specific address onthe data network). The instruction message may include the informationnecessary to construct a packet. For example for IP packets theinformation may include any one or more of the destination address,destination port, number of channels in group and slot details of eachmedia channel of the group. For other protocol types other informationor addresses will be required.

The controller may be located remotely from the processor and/or thetransmission ports on the data network. In this way the controlling ofthe packetizing of the media channels can be performed remotely on thedata network, such as on a separate computer connected to the datanetwork.

If the format of a media channel changes, the controller furtheroperates to automatically re-group the media channels into groups havingthe same format.

In a further aspect, the invention a method for transmitting mediapacket streams on a data network, the method comprising the steps of:

-   -   receiving media channels at a plurality of input media channels,        each media channel having a format;    -   grouping one or more received media channels having the same        format or grouping one or more media channels according to        instructions received on which media channels comprise a group;    -   automatically providing instructions to a processor to packetize        media channels of a group into the same media packet stream; and    -   transmitting the media packet streams.

In another aspect, the invention is an instruction message sent from acontroller to a processor of a transmitter device. In yet a furtheraspect, the invention is a software program to perform the methoddescribed above.

In yet a further aspect, the invention comprises an instruction messagesent from a controller of a receiver device to a controller of atransmitter device, the transmitter device operable to dynamicallyconfigure media packet streams.

In another aspect, the invention comprises a computer system comprisedof a transmitter device and receiver device described above.

In yet another aspect, the invention provides a transmitter device fortransmitting media packet streams on a data network, the transmitterdevice comprising:

-   -   a plurality of input media channels to receive media channels,        each media channel having a format;    -   one or more transmission ports to transmit media packet streams;    -   a processor to packetize received media channels to create media        packet streams for transmission by the transmission port; and    -   a controller to control the processor to create a first media        packet stream containing one or more media channels having the        same format, and to create a second media packet stream        containing one or more media channels having the same format,        wherein the format of the media channels of the first media        packet stream is different to the format of the media channels        of the second media packet stream.

The controller may also automatically determine the number of frames perpacket of each packet stream, wherein the number of frames per packet ofthe first packet stream is different to the number of frames per packetof the second packet stream. Each frame of a packet includes one sampleof each media channel. The number of frames per packet may be determinedbased on the sample rate and bit depth of the media channels within thatgroup.

The controller may also further control the processor to cause the firstmedia packet stream to be sent to a multicast address, and the secondmedia packet stream may be sent to a unicast address.

In yet a further aspect the invention provides a method for transmittingmedia packet streams on a data network, the transmitter devicecomprising:

-   -   receiving media channels at a plurality of input media channels,        each media channel having a format;    -   controlling a processor to create a first media packet stream        containing one or more media channels having the same format,        and to create a second media packet stream containing one or        more media channels having the same format, wherein the format        of the media channels of the first media packet stream is        different to the format of the media channels of the second        media packet stream; and    -   transmitting the created media packet streams.

The invention further provides computer software for transmitting afirst and second media packet stream as described above.

In another aspect, the invention provides a receiver device forreceiving media packet streams from a data network, the receiver devicecomprising:

-   -   a data interface to receive a first media packet stream and a        second media packet stream, wherein each packet of the first and        second media packet streams contain one or more media channels;    -   a processor to extract the media channels from the first and        second media packet streams; and    -   a controller to receive information on the format of the media        channels contained within the first and second media packet        streams, wherein the format of the media channels contained        within the first media packet stream is different to the format        of the media channels contained within the second media packet        stream; and to provide instructions to the processor on how to        de-packetize the first and second media packet steams according        to the different media channel formats.

In yet a further aspect the invention provides a method for receivingmedia packet streams from a data network, the method comprising thesteps of:

-   -   receiving a first media packet stream and a second media packet        stream, wherein each packet of the first and second media packet        streams contain one or more media channels;    -   receiving information on the format of the media channels        contained within the first and second media packet streams,        wherein the format of the media channels contained within the        first media packet stream is different to the format of the        media channels contained within the second media packet stream;        and    -   providing instructions to a processor on how to de-packetize the        first and second media packet steams according to the different        media channel formats to cause the processor to extract the        media channels from the first and second media packet streams.

The invention further provides computer software for receiving a firstand second media packet stream as described above.

In a further aspect, the invention provides a computer network fortransmitting and receiving media packet streams, comprised oftransmitting and receiving devices as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described with reference to theaccompanying drawings in which:

FIG. 1 is a schematic diagram of a network that can be used with theinvention;

FIG. 2 a schematic diagram of a network using a unicast protocol inaccordance with a first embodiment of the invention;

FIG. 3 is a flow diagram of the method of the embodiment shown in FIG.2;

FIG. 4(a) is an example display of a user interface;

FIG. 4(b) is a schematic diagram of single packet of a packet streamsent on the network using the invention;

FIG. 5 is a schematic diagram of a network using a multicast protocol inaccordance with a second embodiment of the invention;

FIG. 6 is a flow diagram of the method of the embodiment shown in FIG.5;

FIG. 7 is a schematic diagram of the network using redundant interfacesin accordance with a third embodiment of the invention;

FIGS. 8(a) to 8(d) is a schematic view of how redundancy can beimplemented in the data network; and

FIG. 9 is a further schematic diagram of a network using redundantinterfaces in according to a fourth embodiment of the invention.

BEST MODE OF THE INVENTION

Overview of the Components of the Network

Referring first to FIG. 1, a data network 100 comprises a transmitterdevice 110 and a receiver device 112. There may be a plurality oftransmitter devices 110 and receiver devices 112 on the network 100, butonly one of each is discussed here for clarity. Further, the devices 110and 112 may be able to perform both transmitting and receivingfunctions, but they are described here as only performing one functioneach again for better clarity.

The transmitter device 110 and the receiver device 112 are connected toeach other by a network 114 so that they are able to send and receivedigital media packets. The transmitter device 110 is comprised of anAudio Processing Engine (APE) 120 and an Audio Processing EngineController (APEC) 122. The receiver device 112 is also comprised of anAPE 124 and an APEC 126. The media packets are sent in media packetstreams that can contain two or more media channels. For simplicity, theembodiments describe all media channels in a media packet stream to bethe same format however the invention can accommodate for multiple mediachannel formats within the one media packet stream.

A media device 140, such as a guitar, is connected to the APE 120 andthe APE 120 receives the media signals generated by the media device140. A preprocessor (not shown) may be added to convert the mediachannel from analogue to digital or convert from one digital format toanother (e.g. sample rate or bit depth conversion). The APE 120 thenpacketizes the digital media channel. The resulting packet stream issent using the network 114 to the APE 124 of the receiver device 112.The APE 124 then de-packetizes the digital media signal, (if suitable)converts it to analogue and transmits the analogue media signal to themedia device 142, such as a speaker for playout. Conversion will not benecessary when the media signals are non-analogue sources, such as aMIDI sources. The rate and offset of packetization and transmission istightly controlled in time to ensure that the playout of the mediasignal by the media device 142 is synchronized with the playout of themedia signals by another media device (not shown) connected to thenetwork 114 that also received the media signal from the APE 120. Thepacketization operation of the APEs 120 and 124 is described in detailin the co-pending PCT application PCT/AU2006/000538 (WO 2006/110960).

An APEC 122/126 is a component implemented in software or hardware. Inthis network 100, the APEC 122/126 is on the same physical device as theAPE 120/124, but alternatively may be located remotely from the APE120/124 such as on another device or a central computer connected to thenetwork 114. An APEC 122/126 provides the user with an abstract view ofthe APEs 120/124 and any audio devices 140 and 142 connected to them. Atransmitter device 110 has a number of transmittable channels that canbe named and then made available to receiver devices 112 on the network114; this is called advertisement. A receiving device 112 has a numberof receiving channels. A named transmitting channel can be assigned to areceiving channel; this is called subscription. APECs 122 and 126 willconfigure the APEs 120/124 to cause the media signals to be routed fromthe transmitting channel to the receiving channel.

The receiving and transmitting APECs 126 and 122 exchange configurationinformation and control messages over the network 114. Configurationinformation is exchanged via a service discovery database 118, such asDNS-SD. This database may be implemented in a distributed manner witheach device 110 and 112 storing and providing the configurationinformation associated with its APEC 122/126. Additional controlmessages are sometimes required to complete the subscription process andcause media signals to be routed. These are sent between the receivingAPEC 126 and the transmitting APEC 122.

Each APEC 122/126 configures its own APE 120/124 and interacts withother APECs 122/126 to ensure that configurations match betweencommunicating APEs 120/124.

Inside each device 110 and 112, input channels such as the channel fromaudio device 140 are known as “TX channels” because they will betransmitted over the network, and output channels such as the channelthat is sent to audio device 142 are known as “RX channels” because theywill receive data from the network.

Unicast Example

In reference to FIGS. 2 & 3, the operation of the computer network ofFIG. 1 in accordance with one embodiment of the invention will now bedescribed. The same reference numbers have been used in FIGS. 1 and 2 torepresent the same components of the network. In this embodiment thecomputer network 104 operates using a unicast protocol.

Connect Up Network

Initially, the devices must be connected 500 to create the network 104.In this case four media devices, a keyboard 144, a guitar 140, a leftchannel for a CD 146 and a right channel for a CD 148, are connected tothe four input channels of the transmitter device 110. The four physicalchannel inputs are labelled channels 1 to 4 respectively. In thisexample the keyboard and guitar use the same sample rate and sampleformat (say 48 kHz, 24 bit, PCM encoded). The CD channels have adifferent sample rate and sample format (say 44.1 kHz, 16 bit, PCMencoded). The output channels of the mixer 112 are connected to a mixingconsole 145.

Both devices 110 and 112 use some mechanism to configure addresses ontheir network interface. One such mechanism is zeroconf link-localaddressing. Each device 110 and 112 randomly picks an address from aspecific range and then checks the network 114 to see if anyone else isusing the same address by using the address resolution protocol (ARP) toquery who owns that address. If no device responds then the address isconsidered unused and it is safe for the device 110 or 112 to claim itfor its own use. In this example the transmitter 110 interface 130 hasaddress 169.254.10.11 and the receiver device's 112 interface 132 hasaddress 169.254.28.12. In this example each device 110/112 has a singleinterface that is shared between their APEC 122/126 and APE 120/124 forprimary data and for configuration, although they could be separate. Inthis example there are no redundant interfaces (redundant interfacesdiscussed further below).

Assign Names

Next, each device and channel is given names 502 as appropriate. As withall configurations, names are stored in the APECs 122 and 126. Each APEC122 is initialized with a default name. One method of choosing a uniquedefault name is a short description such as manufacturer and productname followed by the device's serial number. Users may use a userinterface 149 to change the name stored on the APEC 122 and 126. In thisexample, the interface 149 is provided by a PC that is connected to thenetwork 114 and is presented to the user on the screen of the PC.Channels are variously identified as numbers starting from 1, andarbitrary numbers defined by the APE 120. This step involves givingdescriptive textual names to channels and devices as required, forexample input/TX channels are the only channels given textual names.

The transmitter device 110 is named “stage-box”. The four input channelsare also named. The name “keyboard” is given for the input channel 1connected to the keyboard 144. The name “guitar” is given for the inputchannel 2 connected to the guitar 140. The name “CD-left” is given forthe input channel 3 connected to the left channel for the CD 146. Thename “CD-right” is given for the input channel 4 connected to the rightchannel for the CD 148.

The receiving device 112 is named “mixer”. The receiver device 112 haseight output channels numbered 1 to 8. Since they are output channelsthey are not referenced in any exchange of messages between the APECs122 and 126 they are not given any names for advertisement. For thepurpose of this example, the receiving device 112 does not have anyinput channels connected to a media device.

The APEC 122 presents its TX channels to the user interface 149 as asingle contiguous array, starting from 1. Each presented TX channel alsohas presented an associated name. The names are used duringadvertisement and subscription as described below. In this way, theuser's configuration interactions are based on the textual names of thechannels and devices. This makes configuration from the user'sperspective more user friendly. The APEC 126 presents its RX channels tothe user interface 149 as a single contiguous array, starting from 1 to8.

The APEs 120 and 124 give each of their physical channels an arbitraryidentifier. It is the job of the APEC 122 and 126 to map these physicalidentifiers to the other representations such as the arrays of channelsand names for TX channels. APEs 120 and 124 guarantees that the numberand identifiers of its physical channels are fixed for a given run, butthe (constant) identifiers may occur anywhere in the given space. It ispossible to reconfigure the hardware offline and the APEC willaccommodate the new configuration when it is restarted.

Assume that stage-box's APE 120 identifies its four input channels as16, 17, 32 and 33. Stage-box's APEC 122 represents these identifiers asinput channels 1-4 and associates the appropriate names. Mixer's APE 124has eight output channels numbered 8-15. Mixer's APEC 126 representsthese as output channels 1-8.

Further, the APEC 122 can support TX channel aliases. This means thatthe same physical channel is represented as two different channels withdifferent names by the APEC 122. For example, stage-box's 110 physicalchannel ID 16 might be both channel 1 named “keyboard” and channel 5(not shown) named “lead melody”. Aliases can be added or deleted by theAPEC 122. Aliases are added to the end of the otherwise fixed array ofinput channels.

As part of unicast advertisement, each APEC 122 and 126 needs a uniqueidentifier to refer to a channel. Normal practice is to simply use theAPE's channel ID.

This unicast example uses dynamic bundle configuration. Dynamic bundleconfiguration means that no bundles (and thus packets) are created untila receiver 112 asks for them by way of subscription (as describedbelow). APEC 122 does not initially configure any bundles on the APE120. Dynamic bundle creation requires a configuration port on thetransmitter 110. This port accepts bundle creation requests from thereceiver 112. In this example, stage-box 110 has set up UDP/IP port14481 as its configuration port. The address is stage-box's address:169.254.10.11.

Unicast Channel Advertisement

The next step is the advertisement 504 of the TX channels by stage-box110 onto the network 114. When a TX channel is advertised by atransmitter 110, other receiver devices 112 see it as a “networkchannel”.

Stage-box 110 creates a channel advertisement for each active TXchannel. Each channel has a network name formed by concatenating thechannel's name with the device's name, for example “keyboard@stage-box”.Since “stage-box” is unique on the network 104 and “keyboard” is uniqueon stage-box 110, this network name is guaranteed to be unique on thenetwork 104.

The channel advertisement has four parts as shown here for keyboard:

-   -   Channel network name: keyboard@stage-box. This is used as a        search key by service discovery 118.    -   Channel format. In this case 48 kHz, 24 bit, PCM encoded.    -   Dynamic bundle configuration information. In this case, the        configuration port is stage-box.local:14481. “stage-box.local”        is the unique name that identifies the address of stage-box's        configuration interface 130. It resolves via DNS to        169.254.10.11. Stage-box 110 can handle up to four channels per        dynamic bundle.    -   Existing static (multicast) bundles containing this channel. In        this example, there are no static bundles.        Subscribing

Next, the mixer 112 subscribes 506 to the network channels advertised bythe stage-box 110. Subscription occurs when a receiver 112 associates a(remote) network channel with a (local) RX channel.

A user configuration tool such as the interface 149 can browse theavailable network channel advertisements 506(a) and use these names toconfigure subscriptions on the receiver. In this example, the mixer 112has been configured so that RX channel 1 is subscribed tokeyboard@stage-box, RX channel 4 is subscribed to guitar@stage-box, andRX channel 7 is subscribed to CD-right@stage-box. Notice that the RXchannel numbers (on the receiver 110) and the TX channel numbers (on thetransmitter 112) are independent. The following table summarizes themixer's 112 channel configurations:

RX Channel Subscribed to . . . 1 keyboard@stage-box 2 — 3 — 4guitar@stage-box 5 6 — 7 CD-right@stage-box 8 —

FIG. 4(a) shows how this can be displayed to the user on the userinterface 149.

The receiver 112 now needs to connect the subscribed channels and thuscomplete subscription. The first stage of this process is resolving eachnetwork channel name which is used as a key in service discovery 118,which may be a database that is accessible devices on the network 114.The database stores for each network channel name the correspondingdetailed advertisement. The receiver 112 passes 506(b) each networkchannel name to the service discovery system 118 and receives back thematching detailed advertisement (if it exists).

Using DNS-SD as the service discovery protocol, a network channel'sadvertisement would be received as follows in the example ofkeyboard@stage-box:

Record: keyboard@stage-box._netaudio_chan._udp.local SRV

-   -   0 0 14481 stage-box.local

Record: keyboard@stage-box._netaudio_chan._udp.local TXT

-   -   txtvers=2    -   rate=48000    -   bits=24    -   enc=1    -   nchan=4    -   id=16

“keyboard@stage-box._netaudio_chan._udp.local” is the full name of thekey for the channel advertisement. The SRV record is the primary recordfor the channel. It includes the address and IP port of the dynamicbundle configuration port. The TXT record contains detailed information,including the sample rate, bit depth and encoding (1=PCM). The “txtvers”field is a version number for the TXT record. The “nchan” field is themaximum number of channels per dynamic bundle. Stage-box 110 has amaximum of four channels per dynamic bundle, enough to send all inputsin a single packet. The id field is an arbitrary physical channelidentifier used by the APE 120 to tersely identify its channels. Thechannel named “keyboard” happens to have ID 16. Outside the transmittingAPEC 120, this ID is only useful to a receiver APEC 124 configuring adynamic bundle on APEC 122.

In this example, mixer 112 will ask the service discovery for threekeys: keyboard@stage-box, guitar@stage-box and CD-right@stage-box. Itwill receive three detailed advertisements back from the servicediscovery system 118, one for keyboard@stage-box, one forguitar@stage-box and one for CD-right@stage-box. The mixer's 112 APEC126 now groups 505(c) these advertisements by channel format andconnection method. Since channels guitar and keyboard have the samechannel format and the same dynamic creation port, the APEC 126 createsone group for the two channels (c1). A separate group is created forCD-right@stage-box since it has a sample rate that is different tokeyboard@stage-box and guitar@stage-box (c2).

Because the unicast protocol used in this example is based on dynamiccreation, the receiver 112 needs to nominate 505(d) a destinationaddress and port. The destination address will be the address mixer's112 own interface 132 (169.254.28.12), since that interface is used forprimary data. In some cases, the APEC 126 may choose its own destinationport but in this example the APEC 126 does not, so the APEC 126 choosesto use port 26528 for group c1 and 26719 for group c2.

Mixer 112 must now create pairs of bundles for each group: an RX bundleon its own APE 124 and a matching TX bundle on stage-box 110 for eachgroup. As shown in FIG. 4(b), as part of creating a group each channelmust be assigned a sample space 556 in each frame 554 of the packet 550.This is called a slot. Each packet 550 has one slot per channel and thusone sample space 556 per frame 554. Bundle of group c1 has the followingspecification:

-   -   Destination: 169.254.28.12:26528    -   Channel format: 48 kHz, 24 bit, PCM    -   Slots: 2        Bundle of group c2 will have the following specification:    -   Destination: 169.254.28.12:26719    -   Channel format: 44.1 kHz, 16 bit, PCM    -   Slots: 1

The channel maps will be different on each device 110 and 112. For groupc1, on stage-box 110, input channel 1 (keyboard) will map to slot 1 andinput channel 2 (guitar) will map to slot 2. On mixer 112, slot 1(keyboard from stage-box) will map to output channel 1 and slot 2(guitar from stage-box) will map to output channel 4.

For group c2, on stage-box 110, input channel 4 (CD-right) will map toslot 1. On mixer 112, slot 1 (CD-Right from stage-box) will map tooutput channel 7.

Create Local RX Bundles

Locally, mixer 112 sends 506(e) ‘create RX bundle’ message from its APEC126 to its APE 124 for each group. For group c1:

Field Value Notes Destination 169.254.28.12 Mixer's primary datainterface address address Destination 26528 port Interface 0 Primarydata interface is #0 Number of 2 slots Map for slot 1  [8] Array withone element: RX channel 1 Map for slot 2 [11] Array with one element: RXchannel 4For group c2:

Field Value Notes Destination 169.254.28.12 Mixer's primary datainterface address address Destination 26719 port Interface 0 Primarydata interface is #0 Number of 1 slots Map for slot 1 [14] Array withone element: RX channel 7

Notice that the channel identifiers passed in value maps are those usedby the APE 124. On mixer 112, RX channel 1 corresponds to APE 124 RXchannel 8, RX channel 4 to APE 124 RX channel 11 and RX channel 7 to APE124 channel 14.

The channel maps are actually arrays implemented as bit fields, not asingle value. It is meaningful for example to route slot 2 to both RXchannel 4 and RX channel 5, duplicating slot 2 at the receiver 112. Inthis case, the second channel map would be [11,12].

The channel format is implicit in the channels passed in the channelmap. In this example, all channels in the map must have the same format.It is an error to pass channels with different channel formats in asingle bundle creation message.

Create Remote TX Bundle

Mixer 112 cannot create a bundle on stage-box's APE 120 directly.Instead, it asks 506(f) stage-box's APEC 122 to create a bundle onmixer's 112 behalf for each group.

Mixer's APEC 126 sends a message to stage-box's APEC 122 via theadvertised configuration port 14481 for each group. The message fieldsare quite similar to the fields used when configuring the APE 124. Themain difference is that the fields in the channel map are not arrays.Instead, the channel identifier (which is the APE's 120 identifier) fromeach advertisement is used. For group c1 the message from the mixer 112to the stage-box 110 would be:

Field Value Notes Destination address 169.254.28.12 Mixer's primary datainterface address Destination port 26528 Interface 0 Primary datainterface is #0 Number of 2 channels Slot 1 16 ID of keyboard@stage-boxSlot 2 17 ID of guitar@stage-boxFor group c2 the message from the mixer 112 to the stage-box 110 wouldbe:

Field Value Notes Destination address 169.254.28.12 Mixer's primary datainterface address Destination port 26719 Interface 0 Primary datainterface is #0 Number of 1 channels Slot 1 33 ID of CD-right@stage-box

On stage-box 110, the APEC 122 converts the message from the mixer 112for group c1 into a message to create 505(g) the specified bundle onstage box's APE 120.

Field Value Notes Destination address 169.254.28.12 Mixer's primary datainterface address Destination port 26528 Interface 0 Primary datainterface is #0 Number of channels 2 TX Channel for slot 1 16 TX Channel1 TX Channel for slot 2 17 TX Channel 2

The message for group c2 to create 505(g) the specified bundle on stagebox's APE 120 would be:

Field Value Notes Destination address 169.254.28.12 Mixer's primary datainterface address Destination port 26719 Interface 0 Primary datainterface is #0 Number of channels 1 TX Channel for slot 1 33 TX Channel3

Unlike the RX bundle configuration message, only a single channel canmap to a given slot. Once the TX bundles are created on stage-box 110,stage-box 110 will begin sending packet streams to the mixer 122.

Sending Bundle

Now, that the stage-box 110 and mixer 112 are configured to send andreceive the bundles, the sending 508 of the packet streams can nowbegin. A bundle specifies a stream of packets that is sent from thetransmitter 110 to the receiver 112. Unlike the configuration andservice discovery messages described above, the packet stream is highpriority data and very time sensitive. In contrast, it is not uncommonfor service discovery changes to take a couple of seconds to propagate.

Referring to FIG. 4(b), each packet 550 in the stream has a header 552followed by one or more frames 554. Each frame 554 contains one sample556 from each channel in the stream. The number of frames 554 per packet550 is not fixed and can be tuned by the APEC 122. That is, the size ofa frame 554 is dictated by the number of channels included in the bundleand the size (bit depth) of each channel. Then depending on the size ofthe frames a suitable number of frames 554 per packet 550 is chosen.Increasing the number of frames 554 per packet 550 increases latency butimproves network efficiency. Increasing the number of channels per frameimproves network efficiency as long as the receiver needs all thosechannels.

Each packet header 552 contains a standard Ethernet header, a standardIP header and a standard UDP header in addition to the packet data. Thepacket data contains the audio routing header followed by the frames554.

Audio Routing Header

The audio routing header is 9 bytes long and contains the followingfields:

Field Size Notes Version 1 byte  Timestamp 4 bytes Number of secondssince 1 Jan. 1970 (seconds) Timestamp 4 bytes Number of samples sinceseconds value (samples)

The timestamp is the sampling time of the first frame of samples (allsamples in a frame have the same timestamp). Each successive frame has atimestamp 1 sample after the timestamp of the previous frame.

Because the fractional component is given as samples (rather thanmilliseconds or nanoseconds), it is impossible to reconstruct the actualtimestamp without knowing the sample rate of the samples. Thisinformation is provided out-of-band via the service discovery mechanism118. In this example, the sampling rate is 48 kHz.

No size field is included in the audio routing packet header. Thisinformation is available from the upper level headers, which are alwaysUDP/IP.

Frames

Each frame 554 of samples 556 contains a fixed number of samples 556with homogeneous format (24-bit PCM). In this example, each frame wouldbe 6 bytes long. The first 3 bytes are slot 1 and the second 3 bytes areslot 2. According to the c1 TX bundle specification on stage-box, slot 1contains samples from keyboard (channel 1, APE channel 16) while slot 2contains samples from guitar (channel 2, APE channel 17).

If each packet were 10 frames in length then there would be 60 bytes offrames plus 9 bytes of header for a total UDP/IP data length of 69bytes. The sample timestamps would differ by 10 samples (208.33microseconds at 48 kHz) between each pair of packets.

UDP/IP

The UDP/IP destination for each packet is 169.254.28.12 port 26528, asspecified by the TX bundle. Packets are sent at the second highestpriority level; lower than clock packets but higher than any other data.

Multicast Example

In reference to FIGS. 5 & 6, the operation of the computer network ofFIG. 1 in accordance with a further embodiment of the invention will nowbe described. Same reference numbers have been used in FIGS. 1 and 5 torepresent the same components of the network. In this embodiment thecomputer network 105 operates using a multicast protocol.

Unlike unicast, multicast generally requires the transmitter 110 topre-configure bundles and packet streams. The receiver 112 then extractsthe relevant channels. Unlike unicast, multicast receivers 112 do notneed to directly communicate with multicast transmitters 110.

Initially, the connection 500 and naming 502 steps are repeated asdescribed in the above unicast embodiment.

Create Bundle

When using unicast, channels are advertised even though they are beingtransmitted, and bundles are created dynamically. When using multicast,bundles are created statically and they are only advertised when theyare being transmitted. In this example, stage-box 110 will transmit allchannels. Like the unicast example (FIG. 2) the keyboard 144 and guitar140 use the same sample rate and sample format (say 48 kHz, 24 bit, PCMencoded). The CD channels 146 and 148 have a different sample rate andsample format (say 44.1 kHz, 16 bit, PCM encoded). To send all thesechannels the APEC 122 configures two multicast bundles, being one bundlefor each sample rate, bit depth and encoding method. The first bundle(b1) will contain the two channels keyboard 144 and guitar 140, and thesecond bundle (b2) will contain the two channels CD-left 146 andCD-right 148.

Choose Multicast Address and IP Port

Before the bundle can be created, a multicast destination address needsto be assigned 800. The namespace 239.254/16 is reserved for link localmulticast addresses.

A mechanism is used to choose a suitable unique address. One suchmechanism is to use the dynamic DNS database to register a recordcontaining a randomly generated multicast address. If another device hasalready registered that address then a new address is chosen. Thisprocess is repeated until an unregistered address is found. Registeringthis address claims ownership of the address. Here, the address239.254.46.46 is chosen for the first bundle and 239.254.189.72 ischosen for the second bundle. An IP port is also required and the APEC122 chooses 29061 and 29064.

Configure Bundle

Locally, stage-box 110 sends 802 the following two ‘create TX bundle’messages from its APEC 122 to its APE 120:

Field Value Notes Destination address 239.254.46.46 Multicastdestination address Destination port 29061 Interface 0 Primary datainterface is #0 Number of channels 2 TX Channel for slot 1 16 KeyboardTX Channel for slot 2 17 Guitar Destination address 239.254.189.72Multicast destination address Destination port 29064 Interface 0 Primarydata interface is #0 Number of channels 2 TX Channel for slot 1 32CD-left TX Channel for slot 2 33 CD-right

Now that the bundles are created packet streams for each bundle begintransmitting 804. Any receiver capable of receiving multicast can enablereception of address 239.254.46.46 or 239.254.189.72 and receive theappropriate stream. Some network switches can filter multicast trafficso that it is only delivered to devices that are interested (i.e. notfull broadcast).

Packet Format

For example, each frame in a packet of bundle b1 will have two samplesor 6 bytes of audio data. At 10 frames per packet, this will be 60 bytesof data. Adding a nine byte header results in a 69 byte UDP/IP payload.

Multicast Channel Advertisement

The basic structure of a multicast channel advertisement is the same asfor a unicast channel advertisement 806. Rather than populate thedynamic bundle configuration information, the static bundle informationis populated.

Since a given channel may be a member of several static bundles, thedetails of each static bundle are stored in a separate service discoveryrecord in 118; the bundle name is the key for this record. A staticbundle's service discovery record does not describe the individualchannels; this information must be obtained from the channeladvertisements.

A channel advertisement for a channel contained in a static bundlerefers to the bundle name and the slot value is the slot in the staticbundle that this channel occupies.

DNS-SD Implementation

Using DNS-SD as the service discovery implementation, the additionalbundle field in a channel advertisement would appear as follows:

Record: keyboard@stage-box._netaudio_chan._udp.local TXT

-   -   txtvers=2    -   rate=48000    -   bits=24    -   enc=1    -   b.b1=1

The fields relating specifically to dynamic bundles—“nchan” and“id”—have been omitted. In their place is a field “b.b1=1”. “b.”specifies that this field is a static bundle reference. “b1” specifiesthat the name of the bundle is “b1”. The value “1” specifies thatkeyboard occupies slot 1 in the bundle.

The bundle is assumed to reside on the same device as the channel.“keyboard@stage-box” is specified as being part of bundle “b1”, which isimplicitly “b1@stage-box”.

Static Bundle Advertisement

Like channels, bundles are advertised 806 as “name@device”. However, asingle bundle advertisement might resolve to several different bundles,each of which has the same format but a different destination address(see the discussion on redundancy discussed below).

The bundle advertisement has four parts:

-   -   Bundle network name: b1@stage-box. This is used as a search key        by service discovery.    -   Bundle channel format. In this case b1 48 kHz, 24 bit, PCM        encoded. All channels in a bundle have an identical format.    -   Bundle destination address and port: 239.254.46.46, port 29061.    -   Number of slots in bundle. In this case, two.

Only the destination information varies between multiple versions of thesame bundle. All bundles sharing a bundle network name also share thechannel format and number of slots.

The bundle name is an arbitrary identifier used by APEC 122. It is notnormally visible to users, and has no semantic meaning except as atoken. It would be possible to support user configuration of bundlenames via the GUI 149, such as naming the bundle b1“keyboard-and-guitar” using the GUI 149.

DNS-SD Implementation

In this example, there are two bundle advertisements “b1@stage-box” and“b2@stage-box”. Using DNS-SD as the service discovery protocol, a bundleadvertisement for bundle b1 would appear as follows:

-   -   Record: b1@stage-box._netaudio_bund._udp.local SRV    -   0 1 29061 46.46.254.239.mcast.local    -   Record: b1@stage-box._netaudio_bund._udp.local TXT    -   txtvers=1    -   rate=48000    -   bits=24    -   enc=1 nchan=2

All bundles with the same name share a single TXT record. There is oneSRV record per destination address. SRV records do not containaddresses, but instead a target domain name. When stage-box 110 claimedthe address 239.254.46.46 it created a special record. Resolving thisrecord provides the domain name.

Record: 46.46.254.239.mcast.local IN A 239.254.46.46

The “nchan” field is the number of channels (slots) in this bundle.

Subscription

Subscription 808 is handled identically to the unicast example. Like theunicast case, the first action is to select 808(a) and resolve 808(b)the advertisements. Then these selections are aggregated 808(c). Whendealing with static bundles, channels can be aggregated if the channelformats are the same and they share any one static bundle.

Once aggregation is done, the APE 124 can be configured to receivepackets. Because the packets are already being transmitted, there is noneed to request the transmitting APEC 122 to create a new bundle.However, the packets being received may contain unwanted channels.

In this case the APEC 126 selects the channels keyboard, guitar andCD-Right. Detailed advertisements for these channels are obtained usingDNS-SD 118. Through aggregation it is determined that the subscriptionwill be to bundles b1 and b2, but the first slot in b2 will be ignored.The APEC 126 configuration message 808(d) directs the APE 124 to ignorethe CD-Left channel.

Locally, mixer 112 sends 808(d) the following ‘create RX bundle’messages from its APEC 126 to its APE 124 to configure the APE 126 foreach bundle:

Field Value Notes Destination 239.254.48.48 Mixer's primary datainterface address address Destination 29061 port Interface 0 Primarydata interface is #0 Number of 2 channels Map for slot 1  [8] Array withone element: RX channel 1 Map for slot 2 [11] Array with one element: RXchannel 4 Destination 239.254.189.72 Mixer's primary data interfaceaddress address Destination 29064 port Interface 0 Primary datainterface is #0 Number of 2 channels Map for slot 1  [0] Array with noelement: ignore this message Map for slot 2 [14] Array with one element:RX channel 7

The receiver 112 now starts receiving 810 and is able to route for b1slot 1 (keyboard) to RX channel 1, slot 2 (guitar) to RX channel 4. Forb2 slot 1 (CD-Left) is discarded and slot 2 (CD-Right) is routed to RXchannel 7.

Combining Multicast and Unicast

Many transmitters support both multicast and unicast. A channel can beadvertised with both a dynamic configuration port and one or more staticbundles. During aggregation the receiver APEC must determine the bestmethod of subscribing to the selected channels. Generally, a receivershould attempt to configure its APE to receive static bundles inpreference to creating dynamic bundles. However, a device across awireless link (notoriously poor multicast/broadcast performance) mightprefer dynamic bundles.

When there are multiple equally suitable static bundles, the SRV weightfield can be used to choose between them. Bundles with higher weightsshould be preferred to those with lower weights. In this example, allweights are ‘1’. Alternatively, two channels can share one static bundlebut not another. Regardless of weights, the receiver should prefer toconfigure fewer bundles where possible.

Mostly, unicast is configured to use dynamic bundles and multicast isconfigured to use bundles. The opposite is permissible, however. Astatic bundle might be configured unicast to deliberately send data to areceiver that is not on the local network. Receivers need to verify theaddresses of static bundles since the address might not be valid forthat receiver.

Redundancy

Redundancy will now be described with reference to FIG. 9. Redundancy isachieved by duplicating packet streams over different interfaces of anAPE. Redundancy is mainly controlled at the APEC layer. An APEC canprogram a given packet stream on the APE to be sent or received on aparticular data interface. If a particular media packet stream is to betransmitted redundantly then the APEC programs two or more copies of thepacket stream. One copy to be sent from the first interface 130 of theAPE 120, and a second copy of the packet stream to be sent from thesecond interface 136 of the APE 120.

Similarly, the receiving APEC 126 programs its APE 124 to receive a copyon each data interface 132 and 134. Each duplicate packet stream isprogrammed to copy samples to the same output channels. This means thepacket streams are written to the same buffer. Since the samples andassociated time stamps are identical in both packet streams, identicalsamples are processed and overwritten in buffer for the output channel.Normally, this would result in errors and race conditions. Since allredundant bundles contain identical samples synchronized by timestampsit does not matter sample data is written first to the buffer, as onlyone copy of each sample will actually be sent to the output channelsince all duplicates are simply overwritten.

It is also possible to transmit an individual channel redundantly byadding the channel to multiple distinct bundles.

FIG. 8 shows some of the ways in which redundancy can be implemented ona data network. The interfaces can be connected to independent networksor to a single network via multiple paths. Interfaces 138 and 139 inFIG. 8(c) are the second redundant interfaces of the transmitter 110 andreceiver 112 respectively. FIG. 8(d) shows that the one interface on thetransmitter 110 can transmit to separate interfaces on the receiver 112.

APEs and Interfaces

APEs 120 and 124 with multiple channel data interfaces each designateone interface as primary. This is interface #0. Any further (redundant)channel data interfaces are numbered from 1. For example, the APE 124 ofFIG. 7 with one primary 132 and one redundant 134 interface hasinterfaces #0 and #1.

When transmitting or receiving, for simplicity APEs 120 and 124 areconfigured to only send or receive to equivalent interfaces. The primaryinterface 130 on one APE 120 communicates with primary interface 132 onthe other APE 124. Interface 136 #1 on one APE 120 communicates onlywith interface 134 #1 on the other APE 124. And so on. This allows eachAPE interface to be marked externally. On the hardware itself, theprimary interfaces might be colored black, first redundant interfaces asred, secondly redundant interfaces as blue, and so on. This makes iteasy for a user to distinguish between the differing interfaces andensure they are wired correctly during set up 500.

Unicast Redundancy

The field “nred” may be included in an advertisement TXT record. Thevalue indicates the number of redundant interfaces. If omitted, thevalue is treated as zero. A value of zero indicates no redundantinterfaces meaning that the APE supports a primary data stream only. Avalue of 1 indicates a single redundant interface. Values greater than 1indicate multiple redundant interfaces (numbered 1 . . . n).

Rather than send a single dynamic bundle request, the receiving APEC 126may also send one request per redundant interface available on thetransmitter, each with a different interface field. Alternatively, therequest for the redundant stream to the redundant interface may beincorporated into the original request message for the packet stream tothe non-redundant interface.

As shown in FIG. 7, stage-box 110 has a redundant interface 136 (#1) inaddition to the primary interface 130 (#0). The TXT record of thechannel advertisement is now formatted as follows:

Record: keyboard@stage-box._netaudio_chan._udp.local TXT

-   -   txtvers=2    -   rate=48000    -   bits=24    -   enc=1    -   nchan=4    -   id=16    -   nred=1

Mixer 112 also supports a redundant channel. Its primary data interfacehas address 169.254.28.12 (according to the example described above).Its secondary data interface has address 169.254.132.15.

Locally, mixer 112 sends the following ‘create RX bundle’ messages fromits APEC 126 to its APE 124:

Field Value Notes Destination 169.254.28.12 Mixer's primary datainterface address address Destination 26528 port Interface 0 Primarydata interface is #0 Number of 2 channels Map for slot 1  [8] Array withone element: RX channel 1 Map for slot 2 [11] Array with one element: RXchannel 4 Destination 169.254.132.15 Mixer's secondary data interfaceaddress address Destination 28452 port Interface 1 Secondary datainterface is #1 Number of 2 channels Map for slot 1  [8] Array with oneelement: RX channel 1 Map for slot 2 [11] Array with one element: RXchannel 4

Each message configures one received packet stream to one of theinterfaces. The secondary interface 134 (#1) might use the same portnumber as the primary interface 132 or a different one, depending on theAPE 124 design. This example assumes that a different port is chosen.

Just as mixer 112 must create two separate bundles on its APE 124, itmust create two separate dynamic bundles on stage-box 110. The followingmessages are sent to stage box 110 from the APEC 126:

Field Value Notes Destination 169.254.28.12 Mixer's primary datainterface address address Destination port 26528 Interface 0 Primarydata interface is #0 Number of slots 2 Slot 1 16 ID ofkeyboard@stage-box Slot 2 17 ID of guitar@stage-box Destination169.254.132.15 Mixer's secondary data interface address addressDestination port 28452 Interface 1 Secondary data interface is #1 Numberof slots 2 Slot 1 16 ID of keyboard@stage-box Slot 2 17 ID ofguitar@stage-box

Finally, stage-box 110 creates two bundles on the local APE 120 tofulfill these requests:

Field Value Notes Destination 169.254.28.12 Mixer's primary datainterface address address Destination port 26528 Interface 0 Primarydata interface (on stage- box) is#0 Number of channels 2 TX Channel forslot 1 16 TX Channel 1 TX Channel for slot 2 17 TX Channel 2 Destination169.254.132.15 Mixer's secondary data interface address addressDestination port 26452 Interface 1 Secondary data interface (onstage-box) is #1 Number of channels 2 TX Channel for slot 1 16 TXChannel 1 TX Channel for slot 2 17 TX Channel 2Multicast Redundancy

To support redundant multicast, the transmitter 110 creates severaldifferent packet streams and advertises them as separate static bundlesassociated with a single bundle name.

For example, to advertise two copies of bundle b1 as described in theprevious multicast example, one primary 130 and one secondary 136,stage-box 110 would first claim a multicast address for each bundle. Theprimary bundle uses 239.254.46.46 (as the previous example). Thesecondary bundle uses 239.254.98.147. For this example, assume both usethe same port (29061).

Two SRV records are created, one for each packet stream. Since eachpacket stream is identically formatted, only a single TXT record isrequired.

Record: b1@stage-box._netaudio_bund._udp.local SRV

0 1 29061 46.46.254.239.mcast.local

Record: b1@stage-box._netaudio_bund._udp.local SRV

1 1 29061 147.98.254.239.mcast.local

Record: b1@stage-box._netaudio_bund._udp.local TXT

txtvers=1

rate=48000

bits=24

enc=1

nchan=4

If only a single (primary) interface is used, the “priority” field(which is represented as the first number) in the SRV is set 0. Anon-zero priority indicates that the bundle applies to a redundantinterface, in this case interface 1.

Decoding these bundle advertisements allows the receiver to configureappropriate bundles on each interface. The APEC 126 configures the APE124 to receive the primary bundle on the first primary interface 132 andthe second bundle on the secondary interface 134.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described.

-   -   When using static bundles, channels can be assigned to bundles        in any convenient manner. It is also possible to implement        redundancy by creating specific bundles on specific interfaces.    -   Dynamic bundles are usually unicast. Static bundles are usually        multicast. If required, it is possible to configure dynamic        bundles as multicast or static bundles as unicast.    -   A particular channel can be configured to work with both unicast        and multicast. Standard policy is that receivers should prefer        multicast to unicast since the resource requirements have        already been paid for multicast. Individual receivers may        override this policy.    -   Revocation of advertisements is possible. There are certain        rules governing revocation (and address reuse) to ensure that        configured bundles are removed correctly. The revocation rules        are such that the system will continue to operate if the        configuration information becomes temporarily inaccessible.        Existing configurations cannot be changed, but they do not        automatically terminate.    -   Physical channel inputs/outputs could also be implemented in        software, such as in the software of the mixer, they don't have        to be real physical plugs.    -   While these examples assume sampled audio data, the exact same        protocol mechanisms will work for any fixed-size periodic data        stream. Non-periodic or variable sized data can also be        supported with variations to the transport (packet & bundling)        mechanisms.    -   Assigning homogeneous channels to slots is an implementation        convenience. Non-homogenous channel media data with a common        sample rate can be identified in a frame using a start byte and        length.    -   The system can handle any data that can be expressed in the        advertisements. For example, we define an advertisement format        that represents a frame of compressed video. At the simplest, we        could advertise a single video stream utilising the same exact        global timestamps used by the audio packets and then use the UI        to tell APECs (or equivalent) which ones we wanted routed where.        The APECs would discover the available video channels and        automatically arrange the routing. Unlike an uncompressed audio        sample, a frame of compressed video is often not constant size.        However, if each frame contained a size value then a receiving        APEC could request that three such frames from different streams        be placed in each “frame” of each packet and know how to decode        them. A sophisticated advertisement system could even specify a        bundle (and thus packet) format that consisted of one frame of        video followed by several frames of audio, all synchronised even        though they have different sample rates. Mixing frame sizes and        sample rates requires a more complex advertisement scheme.    -   MIDI is an example of non-periodic data. The same interface that        allows a user to abstractly route audio to audio and video to        video can route MIDI to MIDI. Like periodic packets, MIDI        packets would have a timestamp, but there would not be the        expectation of receivers that units of MIDI data would arrive        periodically. Non-periodic data might need a periodic        ‘keepalive’ message to distinguish between a quiet and a        non-functional stream. Non-periodic data can be automatically        aggregated as easily as periodic data as long as there is a flag        to say “none of this data in this packet”.    -   Although using the system only for homogeneous audio makes        advertisement and packet parsing simpler, as shown by the        embodiments of the invention it is not required for the system        to work. The same user interface that allows the user to set up        audio routing requests and then let the system figure them out        will work for any sort of streamed packet data.    -   Algorithms for automatic allocation of addresses are not shown.        Some of these exist already (e.g. link-local unicast); others        need to be specified (e.g. link-local multicast). It is also        possible to use centrally configured addresses (such as via        DHCP).    -   The “unicast mode” behaviour (′dynamic bundles′: receiver        aggregates and creates bundles) can be used with multicast        addresses. Also the “multicast mode” behaviour (′static        bundles′: transmitter sends pre-created bundles and receivers        pick the channels (and thus bundles) they want) can be used with        unicast addresses.

The present embodiments are, therefore, to be considered in all respectsas illustrative and not restrictive.

Claims defining the invention are as follows:
 1. A receiver device forreceiving media packet streams from a data network, the receiver devicecomprising: a data interface to receive media packet streams, the mediapacket streams containing one or more user selected media channels; aprocessor to extract the user selected media channels from the receivedmedia packet streams; and a controller configured to receive informationon a user selection of media channels advertised on the data network,receive information on the transmission source of the user selectedmedia channels to enable the controller to identify which user selectedmedia channels are transmitted from the same transmission source as agroup, and automatically provide instructions to the processorindicating that one or more media packet streams are to be received fora corresponding group and the number of user selected media channels ineach media packet stream; wherein the receiver is further configured toreceive information on whether the user selected media channels can bereceived statically or dynamically, and if the media channels in saidgroup can be received dynamically, the receiver being configured totransmit a request to the transmission source to create a media packetstream comprising only the media channels included in the group.
 2. Areceiver device according to claim 1, wherein the selected mediachannels each have a format and the controller further operates toreceive information on the format of each of the selected media channelsso as to group the selected media channels with reference to the formatof the selected media channels.
 3. A receiver device according to claim1, wherein one or more media packet streams of a group also containsmedia channels that are not the selected media channels of that group.4. A receiver device according to claim 1, wherein the controller isremote from the processor and/or the data interface.
 5. A receiverdevice according to claim 1, wherein information about the transmissionsource includes network parameters of the transmission source.
 6. Areceiver device according to claim 5, wherein the network parametersinclude an IP address and configuration port identifier.
 7. A receiverdevice according to claim 1, wherein the transmission source is atransmitter device.
 8. A receiver device according to claim 1, whereinfor each selected media channel the controller further receivesinformation on the methods by which the selected media channel can bereceived.
 9. A receiver device according to claim 8, wherein the methodby which the selected media channel can be received is within one ormore pre-defined media packet streams using multicast protocol.
 10. Areceiver device according to claim 8, wherein the method by which theselected media channel can be received is on request to the transmissionsource using unicast protocol.
 11. A receiver device according to claim10, wherein the controller further operates to send a request to receivea media packet stream containing the one or more selected media channelsof a group.
 12. A receiver device according to claim 1, wherein thecontroller further operates to determine the preferred method ofreceiving the selected media channel.
 13. A receiver device according toclaim 1, wherein the controller provides further instruction to theprocessor on which output channels the extracted selected media channelsshould be routed to.
 14. A receiver device according to claim 1, whereinthe receiver device comprises two or more data interfaces, and thecontroller provides further instruction to the processor on which datainterface each media packet stream will be received.
 15. A receiverdevice according to claim 14, wherein the controller further operates tosend a request to receive a first media packet stream at a first datainterface and a second media packet stream at the second data interface,wherein samples contained in the first and second media packet streamare the same.
 16. A receiver device according to claim 1, wherein theinformation the controller receives on the user selection of mediachannels is indicative of a unique name of each user selected mediachannel that describes in words the source of the media channel.
 17. Areceiver device according to claim 1, wherein the controller furtheroperates to send an indication of the advertised name of the mediachannel as a look-up-key to a database connected to the data network andto receive the media channel format information for the media channel.18. A receiver device according to claim 1, wherein the media packetstream contains distinct or overlapping media channels having differentbit depths, encodings and sample rates.